Had an interesting issue during and upgrade from TFS 2012 to 2013.2 today. The upgrade of the files proceeded as expect and the wizard ran. It picked up the correct Data Tier, found the tfs_configuration Db and I was able to fill in the service account details.
However, when I got to the reporting section it found the report server URLs, but when it tried to find the tfs_warehouse DB it seemed to lock up, though the test of the SQL instance on the same page worked OK.
In the end I used task manager to kill the config wizard.
I then re-ran the wizard, switching off the reporting. This time it got to the verification step, but seemed to hang again. After a very long wait it came back with an error that the account being using to do the upgrade did not have SysAdmin rights on the SQL instance.
On checking this turned out to be true, the user’s rights had been removed since the system was originally installed by a DBA. Once the rights were re-added the upgrade proceed perfectly; though interestingly the first page where you confirm the tfs_configuration DB now also had a check box about Always On, which it had not before.
So the strange things was not that it failed, I would expect that, but that any of the wizard worked at all. I would have expected a failure to even find the tfs_configuration DB at the start of the wizard. Not have to wait until the verification (or reporting) step